1. Field of the Invention
This invention pertains to a method of forming cavities in metal injection molded parts that cannot be formed by using a hard mechanically extractable core in the mold and particularly is directed to the use of a fugitive core having a different binder than that used to produce the molded part.
2. Description of the Prior Art
Metal injection molding and ceramic injection molding technologies involve mixing a fine particulate material with a binder. When this mixture is in a plastic condition it is injected into a closed mold where it takes on the configuration of the mold cavity. While in the mold cavity, the binder mixture hardens, sets up or gels to a state where the molded part may be removed from the mold cavity.
After the molded part is removed from the mold cavity the binder is removed without distorting or destroying the molding. The molded part is then sintered into a useable condition.
U.S. Pat. No. 5,043,121 describes a process for removing a polyacetal binder from molded ceramic green bodies with acidic gases and is incorporated herein by reference. U.S. Pat. No. 5,531,958 discloses a process for improving the debinding rate of ceramic and metal injection molded products which use a polymeric binder system and is incorporated herein by reference. U.S. Pat. No. 4,721,599 discloses a method of injection molding metal articles using a water-soluble organic binder and is incorporated herein by reference. U.S. Pat. No. 4,113,480 discloses a method of injection molding powder metal parts using a methylcellulose binder and is incorporated herein by reference. For each of these types of binders, polyacetal, polymeric or water soluble organic, a different process of debinding is used after injection molding the part.
Other variations on these processes are disclosed in U.S. Pat. Nos. 5,155,158; 4,158,689; and 4,158,688; each are incorporated herein by reference.
The drawback in the methods of injection molding according to the prior art is that is difficult to form complicated shapes and particularly difficult to form cavities within the molded part.
An object of the invention is to overcome the drawbacks of the prior art injection molding techniques by providing a simple method of forming complicated shapes and cavities in metal or ceramic injection molded parts.